Field of the Invention
The present invention relates to a sludge treatment method and a sludge treatment system.
Description of Related Art
To produce dehydrated sludge from a sewage sludge, a sewage sludge accumulated in a sludge dehydration tank as raw sludge was conventionally processed for drying directly. To explain the procedure specifically using flow chart in the FIG. 1, a dehydrated sludge B (about 80% moisture content in wet weight basis) discharged from a dehydration step STP1 was processed directly at a drying step STP9 to produce a dried sludge J and discharged.
Also, a methane fermentation reduces the drained weight of solid raw sludge, and methane gas or a digestion gases generated in a methane fermentation process can be utilized as fuel.
The configuration comprises a digestion treatment, a dehydrator for dehydration digested sludge, a dryer for drying a dehydrated sludge, and discharging a dehydrated sludge upon completion of a drying step as a dry sludge (Patent Document 1).    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2011-167648.
In the constitution mentioned above, there was the limit for decrease of the solid quantity of a sludge which could be treated in a digestion tank, and there were the present conditions that fuel costs such as LNG fuel or the heavy oil to use to a dryer increased upon dehydration processing for a digestion sludge by a dryer, and drying by a dryer, and exhausting it as a dry sludge.